Microfluidic oscillating tube densitometer for downhole applications

ABSTRACT

Devices, methods and systems for determining one or more properties of at least one fluid sample. A tube configured to receive the at least one fluid sample wherein the tube is placed in a pressure housing. Further, an excitation source configured to generate vibration of the tube whereby a circulation of an electrical current along a portion of the tube is subjected to at least one magnetic field produced by at least one magnet. Further still, at least one vibration sensor that converts vibrations of the tube into a measurement signal. Finally, a processor that receives the measurement signal determines a resonant frequency from the measurement signal using a frequency measuring device to determine a property of the one or more properties of the at least one sample fluid.

RELATED APPLICATIONS

This patent application is a continuation application of U.S. patentapplication Ser. No. 12/493,717 (Attorney Docket No. 60.1848 US NP),filed Jun. 29, 2009, which claims the benefit of U.S. Application Ser.No. 61/169,485 (Attorney Docket No. 60.1848 US PSP), filed Apr. 15,2009, both of which are hereby incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to devices and methods formeasuring fluid properties for oilfield applications and otherindustries, e.g., chemical and food industries. In particular, theinvention relates to the measurement of the density of microfluidicvolumes of fluids for surface and downhole oilfield applications.

2. Background of the Invention

Understanding fluid density and other fluid properties downhole isparamount to petroleum exploration as it enables one to differentiatebetween oil, gas and water [W. D. McCain, Jr., The Properties ofPetroleum Fluids, 2^(nd) ed. (1990)]. Furthermore, it allows one tolocate the oil-water contact line and hence the thickness of the payzone of a formation. As a consequence, it is a must that robust sensorsbe developed that can accurately measure fluid density and other fluidproperties in a harsh environment found in an oilwell. Oilfieldpressures downhole typically range as high as 15,000 psi withtemperatures as high as 150° C., though wells exist with far moreextreme conditions, especially offshore. A further challenge in downholefluid analysis is that it is a challenge to obtain large quantities ofrepresentative downhole fluids due to the ever-present contamination,whether drilling mud or formation water [O. C. Mullins, M. Hashem, H.Elshahawi, G. Fujisawa, C. Dong, S. Betancourt, T. Terabayashi,Petrophysics 46, 302 (2005)]. Hence sensors that can operate with smallquantities of fluid provide a great advantage. Further, Schlumberger hasmade some progress on miniaturizing vibrating tube densitometers asnoted in J. G. Blencoe, S. E. Drummond, J. C. Seitz, and B. E. Nesbitt,International Journal of Thermophysics, 17, 179 (1996).

The vibrating tube densitometer has a well-deserved reputation as theworld's most accurate technology for measuring fluid density among otherthings, both at ambient conditions and at elevated temperature andpressure [J. G. Blencoe, S. E. Drummond, J. C. Seitz, and B. E. Nesbitt,International Journal of Thermophysics, 17, 179 (1996) and R. Laznickovaand H. Huemer, Meas. Sci. Technol. 9, 719-733 (1998)]. It is noted thatthe accuracy is in part due to the simplicity and the robustness of theunderlying physics as well as its suitability to a wide range oftemperature and pressure. For example, a measurement is performed byfilling the tube with the fluid to be measured and the tube is excitedat its resonant frequency by a piezoelectric or electromagnet actuator.Motion and hence the resonant frequency is measured with a piezoelectrictransducer or an electric pickup coil. Adding the mass of suchtransducers decreases the sensor's sensitivity to fluid density as wellas adding to the complexity of the device. Furthermore, the temperaturedependence of these transducers must be incorporated into theinterpretation.

Density of a single phase fluid can be one of the fundamental physicalparameters required to describe fluid flow, either within the reservoiror borehole, as well as determine both the properties of the surfacefacilities and the economic value of the fluid as noted above; it isalso required to provide the volume translation factor for cubicequations of state that are then used for reservoir simulator. A measureof the single phase fluid density within a sampling tool provides areal-time in situ determination of bore-hole fluid contamination as wellas economic value. Immiscible fluids are required or a separator may beneeded to provide the single phase fluid. Measurements with emulsionsmay be performed and it then becomes a matter of knowing the volume ofeach co-mingled phase before the density of the oil can be extracted;this can be achieved with, as an example, coincidence gamma-rayattenuation measurements with a micro Curie source as described bySchlumberger. For most applications outside of equation of stakanalysis, an expanded uncertainty in density of ±0.01·ρ can besufficient.

Moreover, there are many methods that can be used to measure fluiddensity in a laboratory, for example some of these methods are describedby the following: 1) Wagner et al. [J. W. Density in ExperimentalThermodynamics Vol. VI, Measurement of the Thermodynamic Properties ofSingle Phases, Ch. 5, Goodwin, A. R. H., Marsh, K. N., Wakeham W. A.Eds.; Elsevier for International Union of Pure and Applied Chemistry:Amsterdam, 2003; pp 127-235]; 2) Wagner and Kleinrahm [Densimeters forvery accurate density measurements of fluids over large ranges oftemperature, pressure, and density. Metrologia 2004, 41, S24-S39]; and3) Kuramoto et al. [Accurate density measurements of reference liquidsby a magnetic suspension balance. Metrologia 2004, 41, S84-S94].However, Fujii further describes absolute density standards [AbsoluteDensity Standards in Experimental Thermodynamics Vol. VI, Measurement ofthe Thermodynamic Properties of Single Phases, Ch. 5, Goodwin, A. R. H.,Marsh, K. N., Wakeham W. A. Eds.; Elsevier for International Union ofPure and Applied Chemistry: Amsterdam, 2003; pp 191 to 208, and Presentstate of the solid and liquid density standards. Metrologia 2004, 41,S1-5].

Of the above-mentioned methods, the methods that appear most appropriatefor down-hole applications are those that do not rely on the knowledgeof the orientation of the transducer with respect to the localgravitational field. These methods are based on determining theresonance frequency of a vibrating object and have been summarized byMajer and Pádua [Measurement of Density with Vibrating Bodies inExperimental Thermodynamics Vol. VI, Measurement of the ThermodynamicProperties of Single Phases, Ch. 5, Goodwin, A. R. H., Marsh, K. N.,Wakeham W. A., Eds.; Elsevier for International Union of Pure andApplied Chemistry: Amsterdam, 2003; pp 158-168] and in particularStansfeld with descriptions of devices for use at well-heads andpipelines [In situ Density Measurement in Experimental ThermodynamicsVol. VI, Measurement of the Thermodynamic Properties of Single Phases,Ch. 5, Goodwin, A. R. H., Marsh, K. N., Wakeham W. A., Eds.; Elsevierfor International Union of Pure and Applied Chemistry: Amsterdam, 2003;pp 208-225].

There are many geometrical arrangements that have been reported foroscillating object densimeters with the fluid contacting either theouter or inner surface of, what is usually a metallic object. When thefluid is in contact with the outer surface, the measurement is usuallyconsidered intrusive when operated at elevated pressure, but when thefluid is inside the tube it is a non-invasive measurement. Once theparticular device has been selected it remains a task to develop aworking equation, based on the principles of physics, that relates themeasured quantity (in this case frequency) to density and provide ameasurement with an expanded (k=2 or 95% confidence interval).

In view of tubulars used within a Modular Dynamics Tester (MDT) ameasure of density may be best obtained by a vibrating tube. Thevibrating U-tube is one of the plausible geometries, however there areothers [In situ Density Measurement in Experimental Thermodynamics Vol.VI, Measurement of the Thermodynamic Properties of Single Phases, Ch. 5,Goodwin, A. R. H., Marsh, K. N., Wakeham W. A., Eds.; Elsevier forInternational Union of Pure and Applied Chemistry: Amsterdam, 2003; pp208-225]. Tubes offer another advantage for wire-line (as well as othertool conveyance methods and MWD) in that they can be of low mass and bewell suited to sustaining mechanical shock; rapid changes in localacceleration and the resultant application of large forces. Indeed, asthe internal diameter of the tube decreases so does the outer diameterwhile still maintaining the ability to sustain a pressure differenceacross the tube from within. The type of material used to construct thetube and the elastic properties will determine the absolute value of thepressure difference sustainable by a tube wall.

Most densitometers are calibrated using a calibration fluid having aknown density wherein the density is measured at a specifiedtemperature. The problem with trying to obtain a density measurementoutside of a laboratory/controlled environment is that the density ofmost fluids varies with temperature. Presently, many currently designeddensitometers require that the temperature of the calibration fluid mustbe controlled prior to the fluid being injected into the densitometerfor calibration. This means that the calibration fluid must be in acontainer that is temperature controlled so that the fluid will be heldat a constant temperature. It is noted that the piping of the fluid fromthe container to the densitometer must also be temperature controlled toensure that the temperature being pumped does not change in temperatureduring the transition. Thus, controlling the temperature of storedcalibration fluid along with ensuring the temperature of the fluid doesnot change while the fluid is being pumping to the measuring device, canbe both expensive and a difficult process.

There are known examples of varying types of densitometers or the like.For example, U.S. Pat. No. 4,170,128 issued to Kratky et al. (hereafter“KRATKY”), incorporated by reference herein in its entirety, shows adevice comprising a U-shaped bending type oscillator connected with atensioned body responsive to temperature and pressure. However, theabove reference has many drawbacks, such as a geometry that requires alarge quantity of fluid in order to completely replace a fluid that isinitially present in the tube with a second one. Furthermore, it has aninternal volume closer to milliliters rather than microliters, and ageometry that it is not optimized to operate at large pressures.

U.S. Pat. No. 7,263,882 issued to Sparks et al. (hereafter “SPARKS”),incorporated by reference herein in its entirety, shows a densitometerrelating to chemical concentrations, including those of fuel cellsolutions that can be measured by sensing changes in fluid density as afluid sample flows through a microchannel within a resonating tube of aCoriolis-based microfluidic device. While the SPARKS device disclosesthe use of Coriolis-based microfluidic devices for sensing the mass flowrates and densities of gases and gas mixtures, many more improvements inthe sensitivities of such devices are necessary to fully realize thecapabilities of such devices. Further, the SPARKS device discloses anoscillating tube densitometer that is fabricated out of silicon andoperates with microliter volumes of sample fluid. The SPARKS device isunable to operate at pressures much above ambient pressures as thevibrating element consists of a thin-walled silicon tube. Moreover, theSPARKs device is not a device operable downhole and is limited to lowpressure and low temperature.

U.S. Pat. No. 6,378,364 issued to Pelletier et al. (hereafter “PELLETIER'364”), incorporated by reference herein in its entirety, shows adensitometer for determining fluid properties from vibration frequenciesof a sample cavity and a reference cavity. The measurement device ofPELLETIER '364 includes a sample flow tube, a reference flow tube,vibration sources and detectors mounted on the tubes, and a measurementmodule. The sample flow tube receives a flow of sample fluid forcharacterization. The reference flow tube is filled with a referencefluid having well-characterized properties. The reference flow tube maybe pressure balanced to the same pressure as the sample. The measurementmodule employs the vibration sources to generate vibrations in bothtubes. The measurement module combines the signals from the vibrationdetectors on the tubes to determine properties of the sample fluid, suchas density. In particular, to determine the sample fluid density, themeasurement module of PELLETIER '364 measures the difference betweenresonance frequencies of the sample flow tube and the reference flowtube. The density can then be calculated according to a formula.However, the main drawback for the Pelletier device, among other things,is that it requires milliliter-sized volumes as fluid for operation,predominantly discusses measurements with respect to a second tubereferred to as a standard, along with being disclosed as a large device.Further, another major drawback of the PELLETIER '364 reference is thatit is impractical as well as not commercially viable due to the use ofthe reference frequency originating from the idea that there will be asecond vibrating tube in the tool, filled with a fluid of knownproperties or a vacuum. Further still, the PELLETIER '364 referencerequires the reference frequency due to the structure of the device,e.g., affixing a magnet to the tube and detecting with a pickup coil.

U.S. Pat. No. 6,543,281 B2 issued PELLETIER (hereafter “PELLETIER '281),incorporated by reference herein in its entirety, shows a downholevibrating tube densitometer. However, the downhole vibrating tubedensitometer of PELLETIER '281 has an inner diameter of a tube on theorder of 5 mm, leading to a sensor volume of tens of milliliters at aminimum. The PELLETIER '281 has other drawbacks, as mentioned above,utilizes milliliter scale volumes of fluid for operation and requireseither the excitation or detection components to be clamped to the tube,thereby decreasing the sensor's sensitivity.

U.S. Published Patent Application US 2008/0156093 to Permuy et al.(hereafter “PERMUY”), is commonly assigned to the same assignee of thepresent application and incorporated by reference herein in itsentirety, and shows a commercialized densitometer (InSitu Density) forflowline applications. The PERMUY devices shows a sensor device based onthe use of mechanical elements put into vibration in the fluid to bemeasured. However, the sensor device of PERMUY requires severalmilliliters of fluid at a minimum.

Anton Paar is often recognized as the world leader in laboratoryvibrating tube densitometers. A recently introduced model is now able tooperate at 20,000 psi and at elevated temperatures. However, this devicerequires milliliters of fluid to measure density. The Anton Paarreference discloses a device that does not incorporate a pressurehousing so as to operating in a pressure environment. Further, the AntonPaar reference requires milliliter scale volumes of fluid for operationwhich is not suitable for below ground environments.

More recently it has been shown that actuation can be achieved byplacing part or all of the vibrating tube into a magnetic field and bypassing oscillatory current through the tube body itself [J. Herrero-A′lvarez, G. Gonza′lez-Gaitano, and G. Tardajos, Rev. Sci. Instrum. 68,3835 (1997) and R. F. Chang and M. R. Moldover, Rev. Sci. Instrum. 67,251 (1996)]. For example, the Chang and Moldover reference (hereafter“CHANG”) discloses a vibrating tube design that eliminateselectromagnets and appendages attached to tube of the densimeter, andcan operate at elevated temperature. CHANG discloses measurements ofdensity of toluene between 298 K (about 900 kg×m−3) and 575 K (about 600kg×m−3) at pressures below 13.8 MPa. However, there are many drawback tothis device since, first there is no disclosed pressure housing, andsecondly, the disclosed device would suffer from electrical issues sinceno electrical isolators or similar like devices have been incorporated.

Therefore, there is a need for methods and devises that overcome theabove noted limitations of the prior art. By non-limiting example,devices and methods that can provide a high-accuracy densitometer whichis capable of operation under the high temperature, pressure, shock andvibration conditions encountered in a wellbore; which uses a fluidsample volume equal to or less than 100 microliters; and whicheffectively eliminates the errors associated with the effects oftemperature and pressure on the system as well as suppress electricalnoise coming from exterior influences positioned exterior to the device.

SUMMARY OF THE INVENTION

According to embodiment of the invention, the invention includes adevice for determining one or more properties of at least one fluidsample. The device includes a tube configured to receive the at leastone fluid sample wherein the tube is placed in a pressure housing.Further, an excitation source configured to generate vibration of thetube whereby a circulation of an electrical current along a portion ofthe tube is subjected to at least one magnetic field produced by atleast one magnet. Further still, at least one vibration sensor thatconverts vibrations of the tube into a measurement signal. Finally, aprocessor that receives the measurement signal determines a resonantfrequency from the measurement signal using a frequency measuring deviceto determine a property of the one or more properties of the at leastone sample fluid.

According to aspects of the invention, the tube can be structured andarranged to substantially wrap about an axis of the at least one magnetand bisect a height of the at least one magnet. Further, the at leastone magnet is structured and arranged to be approximate to to 30 percentor more of an overall length of the tube filled with the at least onefluid sample. Further still, the tube has a tube geometry shaped fromthe group consisting of one of at least one bend, two or more bends, astraight tube, one or more shapes or some combination thereof. It ispossible the tube vibrates by one of a piezoelectric device,electromagnet actuator or an other vibrating device. Further, the tubevibrates at a frequency characteristic of the one or more properties ofthe at least one fluid sample. The tube includes at least two endssecured by a holding device such that each end of the tube iselectrically isolated from the holding device.

According to aspects of the invention, the holding device can includeone or more fastening device such that each fastening device includes anelectrically isolated device. The one or more property of the samplefluid determined can be one of density, bubble point, thermodynamicphase, or some combination thereof. Further, a volume of fluid sampledcan be one of a microliter, two or more microliters, equal to or lessthan 100 microliters or some combination thereof. It is possible the oneor more fluid sample can be one of a gas, a liquid or some combinationthereof. Further, the one or more fluid sample can include one of one ormore suspended solid, one or more gel or some combination thereof.Further, the one or more fluid sample can be electrically isolated fromone of at least one inlet and at least one outlet. It may be possiblefor the invention to further comprise of the tube fluidly connected toat least one inlet and at least one outlet, wherein an electricalisolating means electrically isolates the tube from one of the at leastone inlet, the at least one outlet, the at least one fluid entering theat least one inlet or the at least one fluid exiting the at least oneoutlet.

According to aspects of the invention, the device may operable in one oftemperatures equal to or less than 350 C or pressures equal to or lessthan 35,000 psi. Further, the device may be able to determine the one ormore properties of the at least one fluid sample while the at least onefluid sample is one of stationary or moving. Further still, the devicemay further comprise of a filter so as to filter the at least one fluidsample prior to entry of the tube. It is also possible the filter caninclude a microporous membrane that separates formation fluid fromaqueous mud filtrate. For example, using a microporous membrane thatseparates formation oil from aqueous mud filtrate (see PublishedApplication Serial No. 2006/0008913 that is assigned to the sameassignee as the present application).

According to aspects of the invention, the device may operate in one ormore mode for vibration. For example, for the U-shape tube, a first modeof the one or more mode for vibration may produce an up and down motion,a second mode of the one or more mode for vibration may produce a sideto side motion, a third mode of the one or more mode for vibration mayproduce a torsional motion. The device can be positioned within a toolsuch as one of a reservoir tool or a tool for oilfield activities.Further, the pressure housing can seal to protect an exterior of thedevice from pressure external to the device so as to operate while in adownhole environment. Further still, the pressure housing may seal toprotect an exterior of the device from pressure external to the deviceas well as electrically isolates the device from stray exteriorimpedances.

According to aspects of the invention, the device can include anelectrically isolated holding device that is one of unitary ornon-unitary for securing one of the tube, the excitation source, the atleast one sensor or some combination thereof. The electrically isolatedholding device may include one or more fastening device wherein eachfastening device is electrically isolated from one of the tube, theexcitation source, the at least one sensor or some combination thereof.Further, the one or more fastening device includes at least one tubefastening device, at least one magnet fastening device, at least oneunit fastening device for securing one of the at least one tubefastening device, the at least one magnet fastening device, or at leastone other fastening device. It is possible the at least one vibrationsensor can be from the group consisting of one of a electrostatictransducer, a piezoelectric transducer, an electric pickup coil, aelectromechanical sensor, an induction coil, an optical device or another vibration sensing device.

According to aspects of the invention, the invention may furthercomprise at least one sensor for sensing one of temperature and pressureof one of a temperature of the at least one fluid sample, a pressure ofthe at least one fluid sample, a temperature of the tube or somecombination thereof. The at least one sensor or the at least onevibration sensor can be in one of physical contact with the tube or notin physical in contact with the tube. The at least one vibration sensorcan be configured to generate vibration of the tube. It is possible theat least one vibration sensor senses a motion of the tube by sensing anelectro-magnetic force (emf) or a emf voltage induced along the portionof the tube as the tube moves with respect to the at least one magneticfield. Further, the induced emf or emf voltage is equal to or less than100 millivolts. Further still, the induced emf or emf voltage is equalto or less than the 100 millivolts as well as requires an amplificationby a factor of approximately in the range of 100 to 1,000 before beingprocessed by the processor. It is possible the measurement signal can bean electrical signal.

According to aspects of the invention, at least one magnet can bestructured and arranged to be approximate to 35 percent or more of anoverall length of the tube filled with the at least one fluid sample.Further, the at least one magnet can be structured and arranged to beapproximate to 50 percent or more of an overall length of the tubefilled with the at least one fluid sample so as to provide for anincreased magnetic field resulting in an increase in accuracy of thedevice. Further still, the excitation source can be from the groupconsisting of one of at least one electromagnetic, at least onemechanical resonator, at least one electrostatic device, at least onepiezoelectric device, or an other excitation device. The excitationsource can be replaced with a different excitation source, wherein thedifferent excitation source is from the group consisting of one of atleast one mechanical resonator, electrostatic device, piezoelectricdevice, an optical device, or an other excitation device. Further, theelectrical current can be one of an alternating current or a pulsatingcurrent. The excitation source can generate vibration of the tube byalternating a direction of the electrical current with time. Furtherstill, the excitation source is one of physically in contact with thetube or not physically in contact with the tube. The at least one magnetcan be shaped as one of a non-curved shape, a box-like shape or arectangular shape. Further, the tube can have a cavity with an internalcavity volume equal to or less than 100 microliters.

According to aspects of the invention, the processor can be configuredto determine one of a vibration frequency response of the tube, avibration amplitude of the tube, a temperature of the at least one fluidsample, a temperature of the tube, one or more temperatures of thedevice, one or more pressures of the device, one or more exteriorpressures of the device. Further, the processor can be configured tostore one or a previously recorded pressure measurement of the at leastone fluid, a previously recorded temperature measurement of the at leastone fluid, a previously recorded temperature of the tube, one or morepreviously recorded temperatures and pressure of the device, one or morepreviously recorded historical data of one or more boreholes or otherpreviously recorded oilfield application data. The processor can also beconfigured to determine one or more amplitude of the excitation source.

According to embodiments of the invention, the invention includes adevice for determining one or more properties of at least one fluidsample in one of a surface environment or a subterranean environment.The device includes a tube configured to receive the at least one fluidsample and an excitation source configured to generate vibration of thetube whereby a circulation of an electrical current along a portion ofthe tube is subjected to at least one magnetic field produced by atleast one magnet. Further, the invention includes an electricalisolating device that results in electrically isolating one of at leastone inlet or at least one outlet to the tube so as to suppresselectrical conductivity coming from exterior influences positionedexterior to the device. Further, the invention includes at least onevibration sensor that converts vibrations of the tube into a measurementsignal. Finally, the invention includes a processor that receives themeasurement signal determines a resonant frequency from the measurementsignal using a frequency measuring device to determine a property of theone or more properties of the at least one sample fluid.

According to embodiments of the invention, the invention includes amethod for measuring one or more properties of at least one fluid samplein a surface environment or a subterranean environment. The methodincludes (a) receiving at least one fluid sample into a container havingan internal fluid volume wherein the container is positioned within apressure housing; (b) vibrating the container with an excitation sourcewhereby a circulation of an electrical current along a portion of thetube is subjected to at least one magnetic field produced by at leastone magnet; (c) sensing the vibration of the container with a vibrationsensor wherein the vibration sensor converts vibrations of the tube intoa measurement signal that is a container vibration frequency; (d)producing a reference signal from a frequency standard that isindependent of the sample container, wherein the reference frequency isrecorded by a processor; (e) communicating the container vibrationfrequency to the processor, wherein the processor determines a frequencyratio between the communicated container vibration frequency and therecorded reference frequency; and (f) converting the frequency ratio tothe one or more properties of the at least one sample fluid.

According to aspects of the invention, the invention includes one ormore properties of the at least one sample fluid that can be a densitymeasurement of the at least one fluid sample. Further, the container caninclude one of a tube or a hollow structure capable of holding the atleast one fluid sample such that the internal fluid volume is equal toor less than 100 microliters.

According to embodiments of the invention, the invention includes asystem for measuring one or more properties such as density of at leastone fluid sample in one of a subterranean environment, a surfaceenvironment or both. The system includes (a) receiving at least onefluid sample into a hollow structure having an internal fluid volumeequal to or less than 950 microliters positioned within a pressurehousing; (b) electrically isolating one of at least one inlet, at leastone outlet or both to the tube with an electrical isolating device so asto suppress electrical conductivity coming from exterior influencespositioned exterior to the device; (c) vibrating the container to obtaina vibration signal having a container vibration frequency andcommunicating the container vibration frequency to a processor; (d)producing a reference signal from a frequency standard independent ofthe container, wherein the reference frequency is recorded by theprocessor; (e) determining a frequency ratio between the recordedreference frequency and the communicated container vibration frequency;(f) converting the frequency ratio to the one or more properties of theat least one sample fluid.

According to embodiments of the invention, the invention includes amethod for measuring one or more properties of at least one fluid samplein a subterranean environment wherein the at least one fluid is in oneof a single phase or mixed phase. The method includes (a) receiving theat least one fluid sample into a container; (b) vibrating the containerto obtain a vibration signal having a container vibration frequency andcommunicating the container vibration frequency to a processor; (c)producing a reference signal from a frequency standard independent ofthe container, wherein the reference frequency is recorded by theprocessor; (d) determining a frequency ratio between the recordedreference frequency and the communicated container vibration frequency;(e) converting the frequency ratio to the one or more properties of theat least one sample fluid.

According to aspects of the invention, the invention includes the one ormore properties of the at least one sample fluid that can be a densitymeasurement of the at least one fluid sample.

According to embodiments of the invention, the invention pertains to themeasurement of the density of microfluidic volumes of fluids and otherfluid properties. The invention describes a rugged densitometer that canoperate over a wide range of temperature and pressure. Present oilfieldoperations include pressures of 30,000 psi or more and temperatures of200 C or more where such a capability is needed. It is conceived thatthe application for the invention would include surface and downholeapplications. There are several examples that illustrate the utility ofan accurate density measurement of microfluidic volume such as at leastone embodiment of the invention. Example 1: During the exploration phasethe recently drilled open hole well is typically filled with drillingfluids that mix with formation hydrocarbons and provide a source ofcontamination. In order to obtain representative formation fluids, aformation evaluation tool, such as Schlumberger's Modular DynamicsTester (MDT) is conveyed into the well via wireline or on drill pipe andthe formation fluid is pumped from the porous rock face into the tool.At early time the fluid predominantly consists of mud, but over thecourse of several hours the contamination level decreases and the fluidbecomes more representative of the hydrocarbons in place. This methodcan be greatly accelerated by using a microporous membrane thatseparates formation oil from aqueous mud filtrate (see PublishedApplication Serial No. 2006/0008913 that is assigned to the sameassignee as the present application), but the rate of fluid separationis significantly less than 1000 microliters/minute, requiring densitysensors that can operate with microfluidic volumes. Example 2: Rock coresamples containing hydrocarbons are often obtained during theexploration phase and transported to the surface for laboratoryanalysis. The volume of fluid contained in these cores is typically lessthan 1 ml. It would be advantageous to be able to displace the fluid inthese cores with a second fluid and measure the formation fluid densityduring this displacement. Again, in order to do so, a density sensorwould be required that could make an accurate measurement withmicroliters of fluid. Example 3: It would be advantageous to run acomplete PVT (pressure-volume-temperature) analysis on mere milliliters(or less) of live oil. In particular such small volumes could be rapidlyswept or scanned through several temperatures. To do so it would benecessary to measure the density in the single and two phases, and itwould be necessary to have a densitometer that could accurately measurethe density of a sample with no more than microliters of fluid. Thus, itis noted the above three examples, acknowledge there is a need, amongother things, for an accurate densitometer that can simultaneouslyprovide a density measurement with microliters of fluid andsimultaneously operate at high pressures and high temperatures as notedabove.

Another advantage of at least one embodiment of the invention is thatthe invention is capable of minimizing the amount of pumped fluidnecessary for the densitometer to accurately report the fluid density.

Further features and advantages of the invention will become morereadily apparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed descriptionwhich follows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention,in which like reference numerals represent similar parts throughout theseveral views of the drawings, and wherein:

FIG. 1 shows a schematic of the vibrating tube clamped between twoplates and wrapped about a permanent magnet such as a SmCo magnet,wherein current is driven through the tube and the resulting Lorentzforce provides actuation to drive the tube in a torsional mode and theresulting emf (Faraday's law) is proportional to the tube velocity,according to embodiments of the invention;

FIG. 2 shows by non-limiting example at least one pressure housing thatmay be used according to at least one embodiment of the invention;

FIG. 2 a shows by non-limiting example, a simplified diagram of asampling-while-drilling logging device of a type described in U.S. Pat.No. 7,114,562 that may be used as a pressure housing, according to atleast one embodiment of the invention;

FIG. 3 shows a direction of magnetic field as indicated by thehorizontal arrow, the torsional mode's motion is indicated by the curvedarrows which are exaggerated for clarity, according to aspects of theinvention;

FIG. 4 shows a torsion resonance mode that is excited due to theoppositely oriented forces of the tube wherein the actual amplitude ofmotion is approximately 10 microns, according to aspects of theinvention;

FIG. 5 shows a plot of density versus resonant frequency for thevibrating tube for several fluids at 25 C and ambient pressure, whereina fit with Equation (3) is superimposed onto the data, according toaspects of the invention; and

FIG. 6 shows a plot of density discrepancy vs density for heptane (red)and toluene (black) such that these measurements were carried out attemperatures as high as 150 C and pressures as high as 10,000 psi andthe accuracy is typically better than +/−0.5 percent, wherein thediscrepancy is plotted against density, according to aspects of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The particulars shown herein are by way of example and for purposes ofillustrative discussion of the embodiments of the present invention onlyand are presented in the cause of providing what is believed to be themost useful and readily understood description of the principles andconceptual aspects of the present invention. In this regard, no attemptis made to show structural details of the present invention in moredetail than is necessary for the fundamental understanding of thepresent invention, the description taken with the drawings makingapparent to those skilled in the art how the several forms of thepresent invention may be embodied in practice. Further, like referencenumbers and designations in the various drawings indicated likeelements.

According to embodiment of the invention, the invention includes adevice for determining one or more properties of at least one fluidsample. The device includes a tube configured to receive the at leastone fluid sample wherein the tube is placed in a pressure housing. Bynon-limiting example, the pressure housing may be an oilfield loggingtool, oilfield tool or a tool used in either subterranean environmentsor on the surface. Further, an excitation source configured to generatevibration of the tube whereby a circulation of an electrical currentalong a portion of the tube is subjected to at least one magnetic fieldproduced by at least one magnet. Further still, at least one vibrationsensor that converts vibrations of the tube into a measurement signal.Finally, a processor that receives the measurement signal determines aesonant frequency from the measurement signal using a frequencymeasuring device to determine a property of the one or more propertiesof the at least one sample fluid.

FIG. 1 shows a schematic of the vibrating tube 200 clamped between twoplates 600 a, 600 b and wrapped about a permanent magnet such as a SmComagnet 250, wherein current is driven through the tube 200 and theresulting Lorentz force provides actuation to drive the tube 200 in atorsional mode and the resulting emf (Faraday's law) is proportional tothe tube velocity. It is noted that motion can be monitored by measuringthe small emf voltage that develops due to Faraday's law (FIG. 1). Theinvention is applicable to high pressures up to 15,000 psi or more andhigh temperatures up to 150° C. or more for determining measurements ina tube having an outer diameter approximate 1/32″ along with a fluidsampling volume of less than 20 microliters. It is noted thattemperatures in some oilfield applications currently may reach 150 C (itis noted the temperatures could be as high as 350 C) along withpressures of 15,000 psi (it is also noted the pressures could be as highas 35,000 psi). Further, the diameter of the tube can be greater or lessand the fluid sampling volume may be up to 1000 micro-liters. Furtherstill, the tubes used in this densitometer, by non-limiting example aremade of stainless steel or other related materials having similarproperties. However, other types of metals can also be used, forexample, titanium or nickel The outside and inside diameters areapproximately 1/32″ (0.03125″) and approximately 0.020″ respectively. AU-shaped tube can either be clamped between two metal plates or brazedinto two metal blocks such as copper, where each “leg” of the tube is ofapproximately length 4.5 cm (FIG. 1), such that the two metal plates orblocks are electrically isolated from the tube by at least one layer ofa dielectric material such as mica. The end of the tube can be bent intoa half circle of an approximate diameter of 1 cm so as to create anapproximate total internal volume of approximately 20 μl (as note abovethe total internal volume may be approximately up to 1000 μl. It ispossible that other shapes of the tube can also contemplated, such as astraight tube or a tube that bent like a cam shaft to take a jog about amagnet. The copper blocks 600 a, 600 b can be secured to a metal plate400 by fastening devices 700 such as, screws and then isolated from theplate with thin mica sheets (not shown) or some other similar isolatingmaterial. A permanent magnet (SmCo, height 1 cm, length 3 cm, width 0.6cm) 250 is placed in the interior of the loop and an alternatingelectrical current is passed through the tube 200. Further, the magnetmay be fastened by magnet fastening devices 500, such as screws or somesimilar magnet fastening means. A typical high pressure fluidic systememploys connects the metal flowline to the electrical ground plane,thereby introducing stray impedances which would alter if not completelyruin the signal used here to measure fluid density. A plastic union canelectrically isolate the vibrating tube 200, rendering the vibratingtube electrically floating. However, the plastic union may not besufficiently reliable under high shock, high temperature, or highpressure environmental conditions, such as downhole conditions. Thus,the may be a need for requiring the development of a high pressurefluidic coupler that can electrically isolated the two coupled tubes,along with being capable of operating in high shock and high temperaturedevice conditions. Electrical connections to the tube 200 are created byeither soldering directly or by fastening a wire to each side with a nutand a screw or by some other fastening devices. Alternatively, the wirecan be connected directly to the metal block in which the tube isbrazed. The magnet 250 can be carefully centered in the loop of the tube200 such that the loop wraps about the magnet long axis and bisects themagnet height (FIGS. 1 and 2). Fluids are fluidly connected to the tube200 such that the tube has at least one inlet and at least one outlet.

FIG. 2 shows by non-limiting example at least one pressure housing thatmay be used according to at least one embodiment of the invention. Inparticular, FIG. 2 illustrates a wellsite system in which at least oneembodiment of the invention can be employed. The wellsite can be onshoreor offshore. In this exemplary system, a borehole 11 is formed insubsurface formations by rotary drilling in a manner that is well known.Embodiments of the invention can also use directional drilling, as willbe described hereinafter.

Still referring to FIG. 2, a drill string 12 is suspended within theborehole 11 and has a bottom hole assembly 100 which includes a drillbit 105 at its lower end. The surface system includes platform andderrick assembly 10 positioned over the borehole 11, the assembly 10including a rotary table 16, kelly 17, hook 18 and rotary swivel 19. Thedrill string 12 is rotated by the rotary table 16, energized by meansnot shown, which engages the kelly 17 at the upper end of the drillstring. The drill string 12 is suspended from a hook 18, attached to atraveling block (also not shown), through the kelly 17 and a rotaryswivel 19 which permits rotation of the drill string relative to thehook. As is well known, a top drive system could alternatively be used.

Also referring to FIG. 2 and according to at least one embodiment of theinvention, the surface system further includes drilling fluid or mud 26stored in a pit 27 formed at the well site. A pump 29 delivers thedrilling fluid 26 to the interior of the drill string 12 via a port inthe swivel 19, causing the drilling fluid to flow downwardly through thedrill string 12 as indicated by the directional arrow 8. The drillingfluid exits the drill string 12 via ports in the drill bit 105, and thencirculates upwardly through the annulus region between the outside ofthe drill string and the wall of the borehole, as indicated by thedirectional arrows 9. In this well known manner, the drilling fluidlubricates the drill bit 105 and carries formation cuttings up to thesurface as it is returned to the pit 27 for recirculation.

FIG. 2 also shows the bottom hole assembly 100 having alogging-while-drilling (LWD) module 120, a measuring-while-drilling(MWD) module 130, a roto-steerable system and motor, and drill bit 105.

FIG. 2 further shows the LWD module 120 being housed in a special typeof drill collar, as is known in the art, and can contain one or aplurality of known types of logging tools. It will also be understoodthat more than one LWD and/or MWD module can be employed, e.g. asrepresented at 120A. (References, throughout, to a module at theposition of 120 can alternatively mean a module at the position of 120Aas well.) The LWD module includes capabilities for measuring,processing, and storing information, as well as for communicating withthe surface equipment. According to at least one embodiment of theinvention, the LWD module can include a fluid sampling device. It ispossible that at least one embodiment of the invention can be fluidlyconnected to the fluid sampling device.

FIG. 2 also discloses the MWD module 130 that can also be housed in aspecial type of drill collar, as is known in the art, and can containone or more devices for measuring characteristics of the drill stringand drill bit. The MWD tool further includes an apparatus (not shown)for generating electrical power to the downhole system. This maytypically include a mud turbine generator powered by the flow of thedrilling fluid, it being understood that other power and/or batterysystems may be employed. In the present embodiment, the MWD moduleincludes one or more of the following types of measuring devices: aweight-on-bit measuring device, a torque measuring device, a vibrationmeasuring device, a shock measuring device, a stick slip measuringdevice, a direction measuring device, an inclination measuring device orsome other measuring type device.

FIG. 2 a shows by non-limiting example, a simplified diagram of asampling-while-drilling logging device of a type described in U.S. Pat.No. 7,114,562, which is incorporated herein by reference, utilized asthe LWD tool 120 or part of an LWD tool suite 120A. The LWD tool 120 isprovided with a probe 6 for establishing fluid communication with theformation and drawing the fluid 21 into the tool, as indicated by thearrows. The probe may be positioned in a stabilizer blade 23 of the LWDtool and extended therefrom to engage the borehole wall. The stabilizerblade 23 comprises one or more blades that are in contact with theborehole wall. Fluid drawn into the downhole tool using the probe 26 maybe measured to determine, for example, pretest and/or pressureparameters. Additionally, the LWD tool 120 may be provided with devices,such as sample chambers, for collecting fluid samples for retrieval atthe surface. Backup pistons 81 may also be provided to assist inapplying force to push the drilling tool and/or probe against theborehole wall.

FIG. 3 illustrates the vibrating tube 200 that can be driven intooscillation by excitation at its intrinsic resonant frequency with aperiodic burst from a current source, for example a current source of0.5 amps. For example, each burst may consist of ten periods ofoscillatory current at the resonant frequency of the tube. The torsionalresonance mode can be excited (FIG. 3) due to the oppositely orientedforces on the two legs of the tube 200 that result from the Lorenz force(product of current, path length, and field strength). Due to the highquality factor, the two lower frequency modes comprised of vertical andhorizontal motion respectively and are not significantly actuated whenthe excitation frequency is near that of the torsional mode. Thetorsional mode (or second harmonic mode) can be chosen for convenience;other modes (as mentioned above, the fundamental vertical mode (divingboard mode) and/or the first harmonic (vertical mode or side to sidemode) could be more practical for different configurations for thesensor. At least one advantage of using the torsional mode of vibrationis that it is not likely to be excited by the vibrations or shockspresent in a downhole environment. The amplitude of the resulting emfvoltage (resulting from Faraday's law, the temporal change in magneticflux through closed path) is of magnitude 2 millivolts which is thenamplified by a factor of 100 before digitizing with a data acquisitionsystem. (FIG. 4).

Referring to FIG. 4, it is noted that as the quality factor was severalthousand or even higher, very little reduction in amplitude can benoticed during the ringdown. Regression was performed with anexponentially damped sinusoidal function from which the resonantfrequency was extracted. The resonant frequency was typically around1000 Hz and the standard deviation of the 1 second measurement wastypically on the order of 0.02 Hz. Other methods are available formeasuring the resonant frequency and will be obvious to one skilled inthe art. For example, one might sweep an excitation frequency through awide range of frequencies and determine which excitation frequencyproduced the largest amplitude. As well, one might count the number ofzero-crossings in a given time, which indicates the resonant frequency.

The resonant frequency f of the vibrating tube densitometer can berelated to the effective spring constant k and the total mass m as:

$\begin{matrix}{f = {\frac{1}{2\pi}\sqrt{\frac{k}{m}}}} & {{Eq}.\mspace{14mu} (1)}\end{matrix}$

The total mass m consists of the mass of the tube m_(tube) and the massof the fluid ρV where V is the volume of the tube and ρ is the fluiddensity. Substituting for the mass and solving for the fluid densityproduces the following equation:

$\begin{matrix}{\rho = {\frac{k}{( {2\pi \; f} )^{2}V} - \frac{m_{tube}}{V}}} & {{Eq}.\mspace{14mu} (2)}\end{matrix}$

Equation (Eq. 2) above can be rewritten with two calibration constantsA(T,P) and B(T,P) where P and T correspond to pressure and temperaturerespectively and it is understood that the density and frequency dependupon the same thermodynamic properties.

$\begin{matrix}{\rho = {\frac{A}{f^{2}} - B}} & {{Eq}.\mspace{14mu} (3)}\end{matrix}$

Referring to FIG. 5, the resonant frequency f of the sensor was firstmeasured with several simple fluids (e.g. hexane, toluene,dichloromethane) at 25 C and at ambient pressure to cover the fulldensity range. The frequency can be seen to decrease as the fluiddensity increases (FIG. 5) and a fit to the data with equation (Eq. 3)allows for determination of A and B (1.224*107 Hz² g/cc and 8.908 g/ccrespectively). It is noted that a source of error may be speculated tooriginate from insufficient knowledge of the fluid density in certaincases, but primarily from imprecision in determining the resonantfrequency using fitting routines.

Still referring to FIG. 5, there are several existing high pressure andhigh temperature (HPHT) calibration techniques that can be found in theliterature [B. Lagourette, C. Boned, H. Saint-Guirons, P. Xans and H.Zhout, Meas. Sci. Technol. 3, 699 (1992) and M. J. P. Comunas, J-P.Bazile, A. Baylaucq, C. Boned, J. Chem Eng. Data 53, 986 (2008)],however a calibration procedure for the present invention, bynon-limiting example, approximates the spring constant to be independentof pressure. The technique employed requires prior measurement of theresonant frequency of the evacuated vibrating tube over the entire rangeof temperatures investigated as well as the same for a water-filledvibrating tube over the entire range of temperatures and pressures ofthe measurement. In practice a sampling of frequency measurements atvarious (T,P) combinations is made and interpolation is performed forvalues in between. For simplification we denote the inverse frequencysquared when the sensor is filled with water and under vacuum aredenoted as (Λ_(w)) and (Λ₀) respectively. The literature values of thedensity of water (ρ_(w)(T,P)) can be obtained from commonly availablesources, such as that provided by NIST. Interpretation resulting fromthe approximation that k has no pressure dependence results in thefollowing equation for the measurement of the unknown fluid densityρ(T,P) [see Lagourette et al. noted above]:

$\begin{matrix}{{\rho ( {T,P} )} = {{\rho_{w}( {T,P} )}\frac{{\Lambda ( {T,P} )} - {\Lambda_{0}(T)}}{{\Lambda_{w}( {T,P} )} - {\Lambda_{0}(T)}}}} & {{Eq}.\mspace{14mu} (4)}\end{matrix}$

We calibrated the vibrating tube by measuring its frequency at severaltemperatures ranging from ambient to 150 C when evacuated. In practice,this was done with the vibrating tube filled with air as the density ofair would produce an offset that could be absorbed into the calibration.It is noted and acknowledge that the density of air (1.2 kg/m³)introduces a systematic offset to our measurements (0.1% on typicalfluid densities), but remembering that the ideal gas law tells us thatthe density of air will change by less than 25% during our experiments,it is noted that this offset is roughly constant and can be absorbedinto the calibration. Further, we measure a difference of 0.08 Hzbetween the sensor filled with air and that under vacuum, which, notproperly accounted for, adds an offset to the measured density of 0.13%.The data were fit with a second order polynomial such that the inverseresonant frequency squared (Λ₀) could be interpolated at anytemperature. Next, the sensor was filled with water and the resonantfrequency was measured at several separate pressures for the sametemperatures such that the inverse frequency squared Λ_(w) could becalculated for any specified temperature and pressure by interpolation.These two simple sets of automated measurements completed thecalibration. Depending upon the pressure and temperature range used, adifferent and more appropriate calibration method might be employed. Thecalibration method described here simply describes that which we foundmost applicable to our application.

Referring to FIGS. 5 and 6, the sensor was next filled with fluids suchas heptane and toluene and a similar set of measurements wereundertaken. FIG. 5 shows a discrepancy plot where the majority of thedata lie between +/−0.3%, while there are a few outliers with a slightlyhigher discrepancy. The measurements occurred at temperatures as high as150 C and pressures as high as 15,000 psi. The average reproducibilityof the measurements was about 0.1%. The standard deviation of the 1second data was approximately 0.03 Hz or better. These data and otherswere acquired over the course of several months to test the sensor'slong-term stability. There appeared to be an upwards drift with respectto time in the resonant frequency thereby biasing to the discrepancydata to be negative. Proper annealing (“burning-in”) of the sensor atmuch higher temperatures has been shown to reduce this to beimmeasurably small.

According to embodiments of the invention, the invention can be a highlyaccurate vibrating tube densitometer fabricated to operate with 20microliters of fluid or up to 1000 microliters of fluid. The at leastone embodiment which discloses miniaturization can accurately detect themotion of the tube without fastening a magnet or pickup coil to thetube, thereby simplifying the design. As noted above, the invention isapplicable to high pressures up to 35,000 psi and high temperatures ashigh as 350 k.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. It isnoted that the foregoing examples have been provided merely for thepurpose of explanation and are in no way to be construed as limiting ofthe present invention. While the present invention has been describedwith reference to an exemplary embodiment, it is understood that thewords, which have been used herein, are words of description andillustration, rather than words of limitation. Changes may be made,within the purview of the appended claims, as presently stated and asamended, without departing from the scope and spirit of the presentinvention in its aspects. Although the present invention has beendescribed herein with reference to particular means, materials andembodiments, the present invention is not intended to be limited to theparticulars disclosed herein; rather, the present invention extends toall functionally equivalent structures, methods and uses, such as arewithin the scope of the appended claims.

What is claimed is:
 1. A logging tool for determining a property of afluid sample, the logging tool comprising: a pressure housing; a fluidsampling device comprising a probe configured to establish fluidcommunication with a formation and to draw the fluid sample into thelogging tool; and a device disposed within the pressure housing fordetermining a property of a fluid sample, the device comprising: a tubein fluid communication with the fluid sampling device; a filterconfigured to separate the fluid sample from aqueous mud filtrate priorto entry into the tube; a current source configured to pass anelectrical current along a portion of the tube; at least one magnetconfigured to apply a magnetic field to the portion of the tube, whereinthe magnetic field generates vibration within the tube when theelectrical current passes along the portion of the tube; a sensorconfigured to generate a measurement signal by measuring anelectromagnetic force voltage that is induced within the tube; and aprocessor that receives the measurement signal and determines theproperty of the fluid sample using the measurement signal.
 2. Thelogging tool of claim 1, wherein the filter includes a microporousmembrane that separates the fluid sample from aqueous mud filtrate. 3.The logging tool of claim 1, wherein the portion of the tube that passesthe electrical current is electrically isolated from the fluid samplingdevice.
 4. The device logging tool of claim 3, further comprising: atleast one union for electrically isolating the portion of the tube thatpasses the electrical current from the fluid sampling device whilemaintaining fluid communication with the fluid sampling device.
 5. Thelogging tool of claim 1, wherein the tube comprises at least one bend.6. The device logging tool of claim 1, wherein the tube vibrates at afrequency characteristic of the property of the fluid sample.
 7. Thedevice logging tool of claim 1, wherein the property of the fluid sampleis density.
 8. The device logging tool of claim 1, wherein the fluidsample is less than 100 microliters.
 9. The logging tool of claim 1,wherein the tube has a cavity with an internal cavity volume equal to orless than 1000 microliters.
 10. The logging tool of claim 1, wherein thedevice determines the property of the fluid sample while the fluidsample is stationary within the tube.
 11. The logging tool of claim 1,wherein the logging tool comprises at least one of asampling-while-drilling tool, a logging-while-drilling tool, and awireline tool.
 12. The logging tool of claim 1, wherein an amplitude ofthe induced electromagnetic force voltage is equal to or less than 100millivolts.
 13. The logging tool of claim 12, wherein the inducedelectro-magnetic force voltage is amplified by a factor of 100 to 1,000before being processed by the processor.
 14. The logging tool of claim1, wherein the processor determines the property of the fluid sampleusing a temperature measurement and a pressure measurement.
 15. Thelogging tool of claim 14, wherein the temperature measurement is atleast one of: a temperature of the tube and a temperature of the fluidsample.
 16. The logging tool of claim 14, wherein the pressuremeasurement is at least one of: a pressure within the tube and apressure of the fluid sample.
 17. The logging tool of claim 1, whereineach end of the tube is secured by a holding device that comprises aplurality of blocks and each end of the tube is clamped between theblocks.
 18. The logging tool of claim 17, wherein the holding devicecomprises an insulating material that insulates each end of the tubefrom the plurality of blocks.
 19. The logging tool of claim 1, whereinthe tool is configured to operate at temperatures above 150° C. and atpressures above 15,000 pounds per square inch (psi).
 20. A logging toolfor determining density of a formation fluid, the logging toolcomprising: a pressure housing; a fluid sampling device comprising aprobe configured to establish fluid communication with a formation andto draw the formation fluid into the logging tool; and a device disposedwithin the pressure housing for determining density of the formationfluid, the device comprising: a tube in fluid communication with thefluid sampling device; a microporous membrane that separates theformation fluid from aqueous mud filtrate prior to entry into the tube;a current source configured to pass an electrical current along aportion of the tube, wherein the portion of the tube that passes theelectrical current is electrically isolated from the fluid samplingdevice; at least one magnet configured to apply a magnetic field to theportion of the tube, wherein the magnetic field generates vibrationwithin the tube when the electrical current passes along the portion ofthe tube; a sensor configured to generate a measurement signal bymeasuring an electromagnetic force voltage that is induced within thetube; and a processor that receives the measurement signal anddetermines the density of the formation fluid using the measurementsignal.